This invention relates to method and apparatus for hydroforming, indie hydropiercing and slug ejecting and more particularly to the manner of hydroforming, in-die hydropiercing and slug ejecting using a die button, backup plunger and slug ejector all mounted in one of two dies that form the hydroforming cavity in which a part is both formed and pierced.
Prior to the present invention, it was known to provide in-die hydropiercing and slug-ejecting apparatus as disclosed in U.S. Pat. No. 5,398,533 assigned to the assignee of this invention. In that apparatus, the hydroforming fluid pressure forming the part is also utilized to blowout and thereby pierce a hole in the part with the aid of a die button mounted in the lower one of the two dies forming the hydroforming cavity. And this is accomplished without jeopardizing the hydroforming process and without incurring significant hydroforming fluid leakage. Such apparatus also has provision for ejecting the slug produced from forming the hole.
In the above U.S. Patent, the die button is mounted in the lower die with an outer end flush with the cavity surface of the lower die at the location where the hole is desired in the part. The desired hole shape is circular and for that purpose the die button has a round, centrally located cylindrical piercing hole with a sharp cutting edge at its outer end. The die button is further provided with a cylindrical bore of larger diameter than the piercing hole and immediately below the latter. And a backup plunger is received in the die button bore having an outer end that is initially positioned in a flush position in the piercing hole with respect to the cutting edge of the latter and then in a retracted or piercing position in the bore below the piercing hole by mechanical means in the form of a cam operated mechanism. And an elastomeric seal received on the plunger below its outer end remains in sealing contact with the die button bore during plunger movement to prevent hydroforming fluid leakage past the plunger during piercing.
The lower die is further provided with an ejection chute that is open at one end to the die button bore and at an opposite end exits this die. And the plunger is further retractable to an ejecting position where the above mentioned plunger seal moves past and the outer end of the plunger is located immediately below the opening to the ejection chute.
In the operation of the above apparatus, the dies are closed about the part to be formed and while the upper end of the plunger is held in its flush position in the die button, hydroforming fluid at a high pressure is supplied to the interior of the part forcing it to expand outwardly and conform to the die cavity and the outer end of the plunger. The plunger is then retracted to the piercing position allowing the hydroforming pressure to blow out a slug through and past the cutting edge of the die button and onto the outer end of the plunger where it then rests free of the larger diameter die button bore.
Following the piercing of the slug, the hydroforming fluid is then exhausted from the part and while the dies remain closed about the part, the plunger is then further retracted to its ejecting position where the slug which is resting thereon is ejected by an ejector mechanism onto the ejection chute and slides down by the force of gravity to exit the lower die.
Since the die button has only one cutting edge it must be replaced with wear. Furthermore, the piercing is performed with the hydroforming pressure used to form the part and thus imposes a significant sealing burden on the plunger to prevent leakage there past. Moreover, since the plunger seal must pass over the opening to the ejection chute, such action can cause excessive wear of the seal forcing its early replacement.
The method and apparatus according to the present invention is a significant improvement over such prior method and apparatus. And in describing the invention, it will be understood that the terms xe2x80x9cprepiercingxe2x80x9d and xe2x80x9chydroprepiercingxe2x80x9d are used herein interchangeably to describe an operation wherein the hydroforming fluid pressure forming the part is utilized to stretch the region in the part to be pierced only partially into a die button without actually piercing or penetrating this region of the part. With the actual piercing then following this operation at a reduced hydroforming fluid pressure to significantly reduce the sealing requirements of the plunger to prevent leakage there past.
With that understanding, the present invention is directed to an in-die hydroprepiercing, hydropiercing and slug-ejecting method wherein a quick change reversible die button insert is fastened to a cylinder fixed in the lower one of two dies that form the die cavity. And a backup plunger is mounted in the fixed cylinder for effecting hydroprepiercing a region of the part, hydropiercing a hole in this thus weakened region, and finally ejecting the slug produced from the piercing. For such purposes, the plunger has a small diameter end portion closely received in the die button, a large diameter end portion located below the lower end of the fixed cylinder and closely received in a moveable cylinder, and an intermediate portion of intermediate diameter closely received in the fixed cylinder. The small diameter end portion of the plunger has an end face that is flush with the die button when the plunger is in a hydroforming/slug-ejecting position determined by the large diameter end portion of the plunger abutting with an adjusting collar that is fastened to and axially adjustable with respect to the moveable cylinder and is abuttable with an inner end of the fixed cylinder. In the plunger hydroforming/slug-ejecting position, the plunger end face together with the outer side of the die button and outer annular edge of the fixed cylinder form an uninterrupted continuation of the die cavity surface in the lower die.
The cylinder in which the large diameter plunger end portion is received is moveable between a hydroforming/prepiercing/slug-ejecting conditioning position and a piercing conditioning position by a hydraulically operated actuator operated with the hydroforming fluid rather than a separate hydraulic power supply. The plunger is moved to and held in its hydroforming/slug-ejecting position during the hydroforming of the part by supplying the hydroforming fluid to the moveable cylinder actuator to extend the moveable cylinder to and hold it in its hydroforming/prepiercing/slug-ejecting conditioning position and also supplying the hydroforming fluid to act on the large diameter plunger end portion to extend and hold the plunger in its hydroforming/slug-ejecting position. While the moveable cylinder remains in its hydroforming/prepiercing/slug-ejecting conditioning position, the pressure in the moveable cylinder is released allowing the plunger to retract to a prepiercing position in the die button by the force of the hydroforming pressure in the part pressing a region of the part outward against the plunger end face and as a result stretching this region of the part partially into the die button and thus weakening this region but not piercing same.
The hydroforming pressure in the part is then reduced to a pressure just sufficient to pierce the weakened region when left unsupported by the plunger. And the plunger is then allowed to further retract to its piercing position in the die button when the moveable cylinder is retracted to its piercing conditioning position by releasing the hydroforming pressure in its actuator. This allows the plunger to again be retracted but now by the force of the reduced hydroforming pressure in the part pressing outward against the plunger end at the previously weakened region and as a result then piercing a slug cleanly from the part and onto the plunger end face to form the desired hole. And because the hydroforming pressure in the part has been significantly reduced for the piercing operation, the hydroforming fluid is less prone to leak past the plunger following the piercing.
A slug ejector is also received in the lower die and is positioned by a hydraulically operated actuator mounted on the lower die. The slug ejector is initially positioned in a hydroforming/slug-ejecting position where the slug ejector abuts with a rigid abutment in the lower die and a face thereof forms a part of the die cavity surface in the lower die. And from this position and following exhausting of the hydroforming fluid from the hydroformed and hydropierced part and removal of the part from the lower die, the slug ejector is moved by its actuator to a slug-retrieving position opposite the outer side of the die button and the plunger end face. The plunger is then returned to its hydroforming/slug-ejecting position with the slug thereon that is then captured by the slug ejector. The slug ejector is then returned to its initial position but now with the slug and the slug ejector then allows the slug to drop onto a chute and exit the lower die by the force of gravity.
Thus, the retracting movement of the plunger end face in the die button to the prepiercing and piercing positions is determined by the moveable cylinder and its attendant hydraulically operated actuator. And the amount of prepiercing can be finely adjusted with the adjusting collar, which is located between the two plunger cylinders.
In a considerably simpler and more compact embodiment, the hydroforming/slug-ejecting position of the backup plunger is determined by the plunger simply abutting with an inner side of the die button on the supply of the hydroforming fluid to act directly on an inner end of the plunger, the prepiercing position is determined by precisely controlling the amount of hydroforming fluid released from directly acting on the plunger, and the piercing position is established by simply exhausting the hydroforming fluid acting directly on the plunger. And thus the positioning of the plunger is effected without an additional plunger cylinder and attendant actuator.
In the present method and apparatus, the slug ejector by being positioned against a rigid abutment during the hydroforming of the part thus eliminates any need for a device such as a cam mechanism to withstand the hydroforming force acting outward through the part on the slug ejector. Furthermore, because the end area of the large diameter end portion of the plunger acted on directly by the hydroforming fluid pressure is substantially larger than the end area of the plunger against which the part is pressed by the hydroforming pressure, the force of the hydroforming pressure acting to hold the plunger in its hydroforming/slug-ejecting position is substantially larger than that acting through the part on the plunger. And thus there is eliminated any need for a device such as a cam mechanism to hold the plunger against the hydroforming force in the part acting outwardly on the plunger. This is quite advantageous recognizing that such a plunger holding device would need to be packaged in the lower die and as a result reduce the strength of this die as well as add significantly to the cost. In addition, there is as earlier mentioned significantly less hydroforming leakage potential at the plunger in that the actual piercing is accomplished with reduced hydroforming fluid pressure in the part.
Further as to the advantages of the present invention, the body of the lower die beneath the die button does not require a slug ejection opening that could substantially reduce the strength of the die in this region. Nor does the plunger require a seal that must pass over an opening to the slug exit chute and suffer excessive wear as a result. Furthermore, the retraction stroke of the slug ejector and the full extension stroke of the plunger provide the slug ejection travel thus eliminating any need for an additional slug-ejecting stroke by the plunger.
In addition, the high water based liquid solution normally used in the hydroforming of the part is also utilized to effect the forced plunger positions thus eliminating any need for an additional hydraulic power supply to perform these functions. And by utilizing the hydroforming fluid to establish the plunger in both its prepiercing and piercing positions, there is prevented premature piercing of the part such as could result from using a separate hydraulic power supply to operate the plunger.
Moreover, the prepiercing can be optimized during tryout to provide a highly reliable and repeatable process for high volume production. In addition, when the die button wears at one of its cutting edges, it can be simply turned over and reattached to the fixed plunger cylinder to present a sharp fresh cutting edge and eventually with wear of the latter cutting edge, the die button can simply be replaced with a new one. In addition, the pierced hole may have various shapes such as circular and flat sided or some other desired shape with the die button and the end of the backup plunger that is received therein shaped accordingly. Furthermore, there is provided the option of establishing the prepiercing and piercing positions of the plunger with and without a separate plunger movement controlling actuator.
The present invention thus provides for economical, highly reliable, hydropiercing and slug ejecting on a high volume production line. For example, producing various parts for a motor vehicle.
It is therefore an object of the present invention to provide a new and improved method and apparatus for in-die piercing and slug ejecting in a hydroforming process.
Another object of the present invention to provide an economical and highly efficient and reliable manner of in-die hydropiercing and slug ejecting wherein the piercing is partially accomplished in one stage during the hydroforming of the part and is finished in a final stage with reduced hydroforming fluid pressure.
These and other objects, advantages and features of the present invention will become more apparent to those skilled in this technical field from the accompanying drawings and following detailed description.